Process for electrolytic oxidation of quinoline to quinolinic acid



Patented Nov. 16, 1948 PRG CESS FOR ELECTROLYTIC OXIDATION EILGFJQUINQEINEZL'TO QUINOLINIOAGID John B. Connandlacob van deKampgwestfield,

N. "J., assignors to .Merck & 00;, N; J .,a corporationiof New Jersey Incr, Railway,

Nd Drawing. 1 Application January 5,.L-1a4e, Serial-No. 639.424 l This invention relates to processes [f or thewelectrolytic oxidation .of. sulfonated, quinoline. to quinolinic. .acid, andthe present application .is. a continuation-in-part of .our.. abandoned applica tion Serial'No. 418,012,.filed November 6,1941.

The. .oxidation-reduction .eifect of electrolysis is -.well known,..b.ut hithertotherehas been .relatively. little application of this principle to .pyridinederivatives.

The .onlyi,reported. application... of electrolytic oxidation. to pyridine derivatives is that of Yokoyama .(Bull. Chemical...Soc.,..Japa n, 7, 691 72 1932) .whooxidized a-picoline indilute sulfuric acid .medium,..at a lead. dioxide. anode, using high currentdensity (5.0,amperes perlsquaredecimeter of anode .surface) Yokoyama reports. that the product .he;iobtained,. contained only. about .20- 30% picolinic acid, together with a numbenof by-products comprisingnammonia, carbon dioxideand tormiciacid, .He=.also showed that picolinic acid is easily destroyed at a lead dioxide anode. The large;proportion of byproducts obtained by Yokoyama indicates the ease with Which-the'pyridyl ring is split.

In a pending application by one of Se rial= .No. 74181313 :filed. November $9.41,- .:now abandoned (of which a. continuatione'ineparta .is being filed concurrently herewith), there is described a process whereby pyridine derivatives are electrolytically oxidized directly. We have now found that if it is desired to oxidize quinoline, the following advantages may be secured if the quinoline is sulfonated before being electrolyzed:

Noxious gases which are evolved when unsulfonated quinoline is used are eliminated to a large extent with sulfonated quinoline, and a cleaner, more easily purified crude quinolinic acid is formed. Also, when unsubstituted quinoline is used, a higher current density is necessary at the start of the electrolysis to overcome a tendency of the lead dioxide to be reduced. When a sulionated quinoline is used, this tendency no longer exists.

According to our invention, sulfonated quinoline is oxidized in about 6 to 12 N sulfuric acid medium at a lead anode coated with lead dioxide, and at low current density, preferably under 2 amperes per square decimeter. We have found a current density range of from to 1 amperes per square decimeter most satisfactory. A lower current density than is used throughout the elec trolysis is necessary near the end of the run to prevent the decomposition at the anode of the quinolinic acid.

"IThe cellused isof .the two compartmenttype, an. acid resistant, diaphragm, Whichmay ,be. of carborundum, .an. acid-resisting silicate, a. .glass cloth, or othenmaterial havingsimilar properties, being used to.separate the anode compartment from the. cathode....compartment. The. cathode compartment is packed with a vporous.atid-Qresisting. substance, such as sand, ,-in.or.der .toreduce its free volumetoa fractionof that .fofthe anode compartment,f and it is kept filledj with.1:1;.(by

volume) sulfuric acid (i. e.,.ab.o.ut 18 N acid),

The anode used in this cell is of .lead,.,coated with lead .dioxideby. electrolysis .for. about 2 to 6 hours in' about 6. N .sulfuric acid; and. is1abo11t.2.4

square. decimeters .in -surface..area,...per.,mol of the .currentefiicienW.during 'the initialstages of the oxidation is very 'lo'w.' When. an .anode. has been activated by any of the methods described above it remains activated and can be used for a number of successive oxidations Without further activation.

The cathode may be of any acid-resisting metal, such as copper, a highly resistant steel, or an alloy known as chromel (composition: nickel 63%, iron 21%, chromium 16%). A non-metal,-

such as graphite, may also be used as a cathode.

During the course of electrolysis, the temperature may be maintained at the desired level by any one of a number of difierent convenient means, such as by means of heat exchange coils placed directly in the cell or by pumping the cell contents through a heat exchanger. Stirring of the anolyte is advisable, and this may be accomplished by any convenient mechanical device, or, if desired, by an air jet placed directly in the anolyte.

The following example illustrates a method of carrying out the present invention, but it is to be understood that this example is given by way of illustration and not of limitation.

Example Quinoline gms.) is sulf-on ated by heating at 180 C. for 20 minutes with four times its Weight of oleum which contains 20% excess sulfur trioxide. The mixture is then cooled, diluted to 400 cc. with distilled water, and placed in the anode com artment of the two-compartment cell described herein.

The anolyte is stirred and maintained at a temperature of 65-75 C. The current density is set at 1.5 amperes per square decimeter of anode surface until 370 ampere hours per mole of sulfonated quinoline have been consumed. The current-density is then reduced to 0.75 ampere per square decimeter of anode surf-ace for an additional 220 ampere hours. The color. which was originally intensely red, fades during the run to pale orange. The cell is emptied, washed and recharged for another run.

The anolyte liquor is combined with the cell washings, and the combined liquors are diluted to 800 cc. with distilled water, and adjusted to pH 3" with sodium hydroxide. The quinolinic acid may be isolated as the copper or'ferrous salt by the additionof copper sulfate or ferrous sulfate from which salts the free quinolinic acid can be obtained by known methods.

Modifications may be made in carrying out the present invention, without departing from the spirit and scope thereof, and we are to be limited only by the appended claims.

We claim:

1. The process of preparing quinolinic acid that comprises reacting an amount of quinoline with about four times its weigh-t of 20% oleum; diluting the resulting mixture of sulfuric acid and sulfonated quinoline to about twice its volume with water and charging to the anode compartment of a two-compartment electrolytic cell having a lead dioxide coated lead anode, oxidizing the sulfonated quinoline by electrolysis at a current density of about 1.5 amperes per square decimeter of anode surface until about 370 ampere hours per mole of sulfonated quinoline have been consumed, then reducing the current density to about 0.75 ampere per square decimeter of anode surface and continuing electrolysis for about 220 ampere hours per mole, and recovering quinolinic acid from the anolyte.

2. The process of preparing quinolinic acid that comprises reacting an amount of quinoline with about four times its Weight of 20 oleum for about 20 minutes at about 180 C., diluting the resulting mixture of sulfuric acid and sulfonated quinoline to about twice its volume with Water and charging to the anode compartment of a two-compartment electrolytic cell having a lead dioxide-coated lead anode, oxidizing the sulfonated quinoline by electrolysis at a current density of about 1.5 amperes per square decimeter of anode surface, and at a temperature of about 65-75 C., until about 370 ampere hours per mole of sulfonated quinoline have been consumed, then reducing the current density to about 0.75 ampere per square decimeter of anode surface and continuing electrolysis for about 220 ampere hours per mole, and recovering quinolinic acid from the anolyte. Y

3. The process of preparing quinolinic acid that comprises diluting the mixture of sulfuric acid and sulfona-ted quinoline, obtained by reacting an amount of quinoline with about four times its weight of 20% oleum for about 20 minutes at about 180 C., to about twice its volume withwater and changing to the anode compartment of a two-compartment electrolytic cell having a lead dioxide-coated lead anode, oxidizing the sulfonated quinoline by electrolysis at a current density of 0.5 to 1.5 amperes per square decimeter of anode surface. continuing electrolysis after about 370 ampere hours per mole of sulfonated quinoline have been consumed for an additional 220 ampere hours per mole at a current density of 0.5 to 0.75 ampere per square decimeter of anode surface, and recovering quinolinic acid from the anolyte.

JOHN B. CONN.

JACOB VAN DE KAMP.

REFERENCES CITED The following references are of record in the file of this patent: 

